Method and device for packaging objects in a weldable film

ABSTRACT

In a sealing/parting means for the side weld ( 42 ) of a film semi-tube ( 13 ) of shrink film, in which items ( 16 ) are wrapped, the film web ( 19 ) consisting of two sandwiched films is fed to a transport and supporting system ( 18 ) comprising two opposing transport belts ( 21, 22 ) where it runs along an elongated, skid-shaped contact surface area ( 34 ) of a heated sealing/parting knife ( 20 ), resulting in the immediate welding zone of the film being preheated before it is fed at the end of this contact surface area to a sealing/parting blade ( 36 ) which parts and welds the film. The sealing/parting blade ( 36 ) has a constricting cutting gap.

BACKGROUND OF THE INVENTION

[0001] The invention relates to a method and a device for packaging items by means of a weldable film and to a sealing/parting knife therefor. It is to be noted that the terms ,,sealing“ and ,,welding“ as used in the following are synonymous.

[0002] In such packaging machines, items, or stacks thereof, are wrapped by a usually heat-shrink packaging film which forms a tube or at least a double-ply running along the the transport direction. They are subsequently closed off lengthwise and, where necessary, also crossswise to a weld, the overhang of which is cut off.

[0003] U.S. Pat. No. 5,282,349 shows a sealing/parting means incorporating a rotating, heatable sealing/parting wheel for welding the film ply and trimming the overhang, this wheel cooperating with a companion wheel.

[0004] Known from EP 1 027 981 A (corresponding to U.S. patent application Ser. No. 09/500,220 of the applicant, filed Feb. 8, 2000), to which reference is made in the following as regards details of the machine, is one such sealing/parting device including a sealing/parting wheel.

OBJECT OF THE INVENTION

[0005] The objective of the invention is to improve the sealing/parting and also to render it useful for films which are difficultt to weld, as well as providing a device which is particularly simple and reliable in operation.

SUMMARY OF THE INVENTION

[0006] The invention provides a method in which, instead of a sealing/parting wheel, a sealing/parting knife is used which is simple to manufacture and is particularly reliable in operation. Unlike a wheel including a flexible companion wheel, the sealing/parting knife works particularly reliably in operation with no wear. Provided upstream of a sealing/parting blade is a preheating zone in which the film is preheated, preferably in a very narrow, strip-type zone, so that when it encounters the sealing/parting blade it is easily parted, on the one hand, and is well suited to welding to the adjoining ply, on the other.

[0007] This method also lends itself to satisfactorily working films very difficult to weld, this applying more particularly to certain multi-ply polyolefine films relatively thick in part, i.e. in the range 30 □m to 120 □m (preferably 60 to 100 □m). Such shrink films extruded multi-ply are marketed by SEALED AIR CORP. CRYOVAC, Rodgers Bridge Road, Building A-Duncan, SC 129334-0464, U.S.A. designated ,,CorTuff“, the standard version of which ,,CorTuff STANDARD“ is 60 □m thick whilst the heavy version of which ,,CorTuff HEAVY“ is 100 to 120 □m thick.

[0008] These films are exceptionally resistant to tearing and are employed for packaging stacks of heavy and large items, for example, construction elements. Welding these films has always been difficult, which is now corrected by the invention. However, the invention can be put to use to advantage for other kinds or grades of film.

[0009] The device comprises a means with which the film is transported relative to a sealing/parting device in a film transport direction, preferably continuously or also discontinuously. The sealing/parting device comprises a preheating zone, followed by a heated sealing/parting blade. Preheating zone and sealing/parting blade may be combined in a common, heatable sealing/parting knife comprising an elongated narrow surface portion running parallel to the running plane of the film at which the film is guided along with contact so that it is heated by contact heat.

[0010] Directly adjoining the latter and heated together therewith the sealing/parting blade may be provided. It crosses the film ply and may form a intake gap formed, on the one hand, by the contact surface area and, on the other, by a protruding blade section, the intake gap protruding under the film ply like the bulbous bow of a ship, as a result of which the film is reliably guided into the cutting zone of the sealing/parting knife. The complete sealing/parting knife is either clamped in a heated support or, preferably, it has an integrated heater and a control sensor. These may be accommodated in corresponding drillings adjoining the working zones formed by the contact surface area and the film welding knife. The sealing/parting means is suited to particular advantage for substantially continuous production of a side weld of a film semi-tube of a shrink film, but is just as suitable also for other applications, e.g. for welding film webs on both sides, etc.

[0011] Details of the film is transport and guide in the sealing/parting zone can be taken from the patent publication EP 1 027 981 A of the applicant as cited at the outset to which express reference is made in the present specification.

[0012] These and further features are evident not only from the claims but also from the description and drawings, each of the features being achieved singly or in combination in the form of sub-combinations in one embodiment of the invention and in other fields and which may represent advantageous aspects deserving protection in their own right as claimed in the present. It is understood that sub-dividing the application into individual sections as well as intermediate titles does not restrict the claims made therein in their general application.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] An example embodiment of the invention will now be detained with reference to the drawing in which:

[0014]FIG. 1 is a diagrammatic view in perspective of part of a packaging machine including a sealing/parting device,

[0015]FIG. 2 is a side view of the sealing/parting device including the corresponding transporting system.

[0016]FIG. 3 is a side view on a magnified scale of a sealing/parting knife,

[0017]FIG. 4 is a front view of the sealing/parting knife and

[0018]FIG. 5 is a further section on a magnified scale taken along the line V-V as shown in FIG. 3

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

[0019] Referring now to FIG. 1 there is illustrated, as part of a packaging machine 11, a side sealing/parting means 12 for the purpose of closing off on one side a film semi-tube 13 in which the items 14, for example books, boxes, but also larger and heavier parts such as doors, windows or the like are to be packaged as described in general U.S. Pat. No. 5,799,470 A to which express reference is made as regards the device for folding the tube 13 and for inserting the items. The film semi-tube 13 thus consists of a web of film longitudinally folded roughly in the middle in which the items are located spaced away from each other. The side sealing/parting means 12 serves to produce a tube from this film semi-tube in which the two webs of film located one on the other, are welded together with simultaneous parting and removal of the waste overhang 15. The film used in this case is preferably the relatively thick polyolefine film as described previously.

[0020] The items are transported on a transport belt or a table substantially continuously in the transport direction 17.

[0021] The side sealing/parting means 12 contains, as evident from FIGS. 1 and 2, its own transport and supporting system 18, the speed of which is synchronized to that of the transport belt, the transport and supporting system 18 feeding the film webs 19 pressed together into a sealing/parting knife 20 and subsequently thereto to the welding zone over a certain distance.

[0022] The transport and supporting system 18 consists of two sets, each consisting of two endless transport belts 21, 22, which are synchronized via meshing gearwheels 23 on their drive and guide rollers 51, 52, 53. Each set of transport belts consists of two belts guided parallel to each other, forming a gap 50 inbetween in which sealing/parting is done, i.e. the film webs are guided tensioned on both sides of the later weld. Each transport belt runs over two rollers 52, 53 at the input end and the drive roller 51 driven by the gearwheel 23 so that it has a triangular path, within which, space is provided for the sealing/parting tool.

[0023] The lower reach 24 of the upper transport belt 21 and the upper reach 25 of the lower transport belt 22 run in contact with each other, separated only by the film webs located inbetween, and are guided, where necessary, via slide rails 26. Before the film enters the side sealing/parting means it passes through an intake roller pair 27. These transport means are synchronized in transport direction and speed with the transport belt.

[0024] The double-ply film web 19 guided between the belts 21, 22 is fed in a film running plane 54 to the sealing/parting knife 20 arranged in the region of the parallel guide afforded by the reaches 24, 25. The sealing/parting knife 20 is releasably and replacably clamped in a support 28 and consists of a metal body as evident more particularly from FIGS. 4 to 5. Near the tensioning tabs 29 and in the region of a relatively massive base body 30, which is elongated in the transport direction, there is an electrical heater cartridge 31 accommodated in a horizontal longitudinal drilling. The cartridge serves to heat the sealing/parting knife and is maintained at a preset temperature by a controller (not shown) for setting to the required temperature as detected by a temperature sensor 32 accommodated in a drilling of the base body 30 parallel to the heater cartridge.

[0025] Adjoining the base body 30, offset to one side thereof, is a relatively narrow skid-shaped contact bar 33 transversely to the transport direction including a narrow and elongated contact surface area facing the film web, comprising in the intake region a rounding 35. At its elongated side edges the contact surface area is provided with a chamfer 36 (FIG. 4) or a radius, it preferably being configured straight and parallel to the transport direction 17, but may also be configured curved.

[0026] The contact surface area is roughly 3 mm (between 2 and 4 mm) wide and has a length of 50 to 100 mm along which the sandwiched film webs 19 run in contact therewith.

[0027] Provided at the end of the contact surface area, i.e. after the film webs 19 have run along the majority of the contact surface area, is a sealing/parting blade 36 incorporating the sealing/parting knife preferably formed as a single piece of metal. As compared to the contact surface area this sealing/parting blade is relatively short (roughly 10 to 15 mm in the direction of the film), it crossing the film web 19 and forming with the contact surface area a constricting intake gap 37 becoming narrower in the transport direction and formed so that the contact surface area also in this portion is still able to pass through substantially in a straight line. This is why the sealing/parting blade 36, although sharpened to an edge at the front, has the shape of a bulbuous bow in the side view so that the film is maintained, in any case, in its predefined film running plane. Reference is expressly made to the Figures, especially to FIGS. 3 to 5. as regards details in configuring the sealing/parting knife and more particularly the sealing/parting blade.

Function

[0028] The items wrapped in the film semi-tube 13 are run, together therewith, past the side sealing/parting means in the film running plane 54 preferably continuously at constant speed, the side sealing/parting means feeding the films tensioned between the transport and supporting belts 21, 22 to the sealing/parting knife which is heated to a temperature permitting sealing/parting as a function of the nature of the film, its thickness etc., more particularly as a function of the melting response of the film as well as of the intake speed of the film. The film enters the zone of the sealing/parting knife 20 in the region of the intake rounding 35 and in contact with and along the elongated narrow contact surface area 34, resulting in the film being uniformly preheated but restricted to the portion of the later sealing/parting seam, i.e. the useful width of the contact surface area, after deduction of the rounding or chamfer, constituting the welding zone which is only few millimeter wide as guided in the gap 50.

[0029] When the film attains the sealing/parting blade 36, the two film webs 19 are parted, whereby welding of the film webs usually takes place already beforehand to a certain degree. In any case, however, the two film webs are welded together downstream of the sealing/parting blade 36, as prompted by the constricting shape of the intake gap as well as by the side guide surfaces 39 of the sealing/parting blade (see more particularly FIGS. 3 and 5) subsequently configured as a wedge-shaped constriction. The film material preheated by the contact heat transfer mainly in the welding zone and thus softened is, after having been parted, urged slightly apart by the thickness of the sealing/parting blade which may correspond at the rear end 40 to that of the contact bar 33, whilst simultaneously being concentrated from above and below to thus enable a reliable weld to be formed.

[0030] The film waste strip 15, likewise welded in this action and likewise consisting of two plies of film, is removed by vaccuum 40 (FIG. 1), although, of course, instead of vacuum removal a reeler could be used just as well.

[0031] Trials have indicated that with this film sealing/parting knife films can also be satisfactorily welded which hitherto were unweldable satisfactorily with other knives or sealing/parting wheels. The reason for this is, on the one hand, the reliable film intake, as assured by the contact rail, to the actual sealing/parting blade, and on the other, by the preheating being restricted particularly to the direct parting site. This is assured by the contact transfer in the region of the contact surface area 34 whose width substantially corresponds to the width as furnished by the material for the sealing/parting weld.

[0032] Once the weld 42 has been produced and thus the film semi-tube 13 created, the latter is fed with the items to a cross welding means which undertakes a sealing/parting action in the interspaces 43 between the items to totally wrap the item and to separate each individual packaged item from the other. After this, the items are run into a shrink tunnel in which the shrink film, of which the packaging mostly consists, is shrunk tight about the items by heating. Because of the forces materializing thereby, it is essential that the weld or sealing seams are resistant to tensile stress and uninterrupted. 

1. A method of packaging items (14) by means of a weldable film (19) in which the film is transported relative to a sealing/parting device (12) in a film transport direction (17) comprising the steps of feeding the film (19) to said sealing/parting device (12) in at least two plies, preheating an area of the film in said sealing/parting device (12) in a preheating zone (34) of said sealing/parting device, subsequently parting said film by means of a heated sealing/parting blade (36) in said preheated film area, thereby creating heated parted edges of the film, and thus simultaneously welding at least two of the plies at the parted edges.
 2. The method as set forth in claim 1 wherein said film area is preheated by contact heat transfer in said preheating zone.
 3. The method as set forth in claim 1, wherein said film area is a narrow, longitudinal area of the restricted to immediate vicinity of said cut portion.
 4. The method as set forth in claim 1, wherein preheating is undertaken in a preheating zone (34) oriented elongated in said film transport direction (17).
 5. The method as set forth in claim 1, wherein said film (19) is a polyolefine film.
 6. The method as set forth in claim 6, wherein said film (19) is a shrink film between 30 and 120 □m thick of the kind as marketed by SEALED AIR CORP. CRYOVAC, Rodgers Bridge Road, Building A, Duncan, SC 129334-0464, U.S.A. designated ,,CorTuff“.
 7. A device for packaging items (14) by means of a weldable film (19) comprising a film transport (16,18), with which said film is transported in a transport direction (17) relative to a sealing/parting device (12), said film (19) includes, when passing said sealing/parting device (12), at least two layers, said sealing/parting device (12) comprises a preheating zone (34) and, following on the preheating zone, a heated sealing/parting blade (36).
 8. The device as set forth in claim 7 wherein of a sealing/parting knife (20) includes said sealing/parting blade (36) and an elongated bar (33) having, with regard to the transport direction, a leading and a tailing end the bar forming said preheating zone, at which said film (19) is guided along in contact in said film transport direction (17), the sealing/parting knife (20) being provided at the tailing end.
 9. A heatable sealing/parting knife (20) for a device (11) for packaging items by means of a weldable film (19), said film being guided in at least two plies in a film transport direction (17) and in a film running plane to said sealing/parting knife (20) and along thereof, resulting in said multi-ply film (19) fed to said sealing/parting knife (20 being parted and thereby welding at least two sandwiched film plies to each other, the knife comprising: a surface portion runmning parallel to said film running plane including an elongated contact surface area (34) facing said film running plane, and an adjoining sealing/parting blade (36) crossing said film running plane.
 10. The sealing/parting knife as set forth in claim 9 wherein said contact surface area has, with reference to said film running direction, a leading end and a tailing end, and has at its leading end, an intake rounding (35) and adjoining thereto a straight strip-type, elongated contact surface area (34) of small size transversely to said film running direction (17) and wherein said sealing/parting blade (36) as compared to said contact surface area portion is short and has a cutting edge (38).
 11. The sealing/parting knife as set forth in claim 9, wherein said sealing/parting blade (36) together with said contact surface area (34) forms a constricting intake gap (37).
 12. The sealing/parting knife as set forth in claim 9, wherein said contact surface area is between 2 mm and 4 mm wide and 50 mm to 100 mm long.
 13. The sealing/parting knife as set forth in claim 9 in which a heater (31) and a temperature sensor (32) are integrated. 